95 YJ 2.5 runs rich, misses at 3k rpm, I have tried a lot

**ritjobbie** · 07-31-2007, 08:48 PM

I have been trolling for a while looking for answers to my engine problems. I have tried a bunch of things that I have seen searching this forum, but none have resolved my problem.

I have a 1995 Wrangler Rio Grande 2.5L 5-spd.

My symptoms:
1) engine runs rich and fuel economy sucketh (those go hand in hand)
2) check engine light reports 52 (O2 sensor sees rich, verified by my nose and eye sensors)
3) engine drives pretty normal except for a little rough idle until 3k RPM. At 3k RPM if I am pushing the accelerator down any harder than about 25%, the engine SERIOUSLY hesitates and seems to missfire.
4) spark plugs are black as death (see #1 and #2)

My initial problem that got this problem train rolling was a bad injector. I got a CEL code for injector not responding to control. Turns out it didn't want to spray anymore. I got new injectors (from 5Omotorsports) that are supposed to be OEM replacements (19lbs., is that right?).

I swapped out the injectors and then I got a few CEL codes: MAP sensor, rich mix on the O2. I changed vacuum lines on the MAP and since haven't seen that code again. I also verified voltages from the MAP while ignition was ON and when car was running. I also verified the throttle position sensor's voltages are good right after I took off and cleaned up the throttle body. I changed my air filter even though I knew the old one was relatively new.

I then read a post about how a fuel pressure regulator can cause a rich mix if it fails. A symptom of this is gas on the vacuum side of the FPR. I swear I could smell gas on the vacuum side so I replaced the FPR. I also put new plugs in at the same time for good measure.

I wonder if my new injectors are spraying too much gas (not sure if 19lbs is the right rating, but they are supposed to be direct replacement), but I would think that the computer would just shorten the pulse and figure everything out if that were the case.

Is there a single problem that would cause rich mix AND missing at 3k RPM? I think I have run out of things to try.

For what it's worth, I made some minor repairs about a month ago, but everything was running fine afterwards for a few weeks. My valve cover gasket was leaking oil on to my starter, causing the starter to die. I replaced the starter and valve cover gasket only to notice that one of my heater core hoses were slowly leaking. I replaced the hoses and everything seemed to be okay. I changed my oil and filter when I replaced my valve cover gasket, about a month ago.

Please help.

Thanks in advance.

**paultyler** · 07-31-2007, 09:02 PM

Dumb question: Have you tried a complete tune up? Plugs, wires, cap. etc.? I see that you changed the plugs.

**ritjobbie** · 07-31-2007, 09:08 PM

Quote:

Originally Posted by paultyler

Dumb question: Have you tried a complete tune up? Plugs, wires, cap. etc.? I see that you changed the plugs.

I did wires, cap, rotor about 5-10k miles ago. I suppose I could try new wires, but I'm pretty sure my distributor is still happy.

**paultyler** · 07-31-2007, 09:19 PM

Quote:

Originally Posted by ritjobbie

I did wires, cap, rotor about 5-10k miles ago. I suppose I could try new wires, but I'm pretty sure my distributor is still happy.

Sweet. I am not a mechanic. But when mine ran rich I was told that a tune up will fix that problem most all of the time. In fact the tune up worked for me.

**ritjobbie** · 07-31-2007, 10:04 PM

I just tested my TPS again to make sure I had the numbers right. It goes from just above 0.5V to just under 4V. Is that normal?

merlin7782 · 07-31-2007, 11:22 PM

I had the problem in a 2.5 and it was the TPS.. I remember pulling the plugs they were black and stunk... I'd try a TPS and if it doesn't work take it back..

**Big-n-Broke-YJ** · 07-31-2007, 11:25 PM

i'd have to say tps or map.....

check your pm's

**ritjobbie** · 08-01-2007, 08:59 AM

Quote:

Originally Posted by Big-n-Broke-YJ

i'd have to say tps or map.....

check your pm's

Thanks for the info. However, I just verified that the voltages I get from my TPS and MAP are both cool. There are no dead-spots in the TPS, either--it's smooth from 0.78V to just under 4V@WOT. MAP goes from 0.6V to just barely over 5V@WOT.

I'm glad this isn't my daily driver, but there is nothing better than summertime in an open-top Jeep.

Eclipse This · 08-01-2007, 09:05 AM

Oxygen sensor could cause it to run rich if i'm not mistaken. Just a thought.

**leftlanetruckin** · 08-01-2007, 09:14 AM

yeah summer time huh?
top down, 37's rolling smoothly on the blacktop, metallica coming from the speakers.....
oh wait, i forgot, my junk is in my shop with the tranny and transfercase out of it...

hopefully will be back together today if the tranny shop comes through for me...
keep at it, you will figure it out in the end..... here's a quick story to make you feel better...
had fluid coming out of the (assumed) tranny vent line after doing my motor/tranny swap...
i ask around, look around, and then pull the motor to replace the t/converter. 2 week later, same deal....fluid coming out of the (assumed)tranny vent line.
ok, i had enough, time to drop the full skid plates, and pull the tranny out of the sob. it was the only thing i didnt completely rebuild when i put the chevy running gear in there...
but wait.... i loosen my transfer case FILL plug, and @2qts of fluid come out!!
the vent line ran from the t/case, not the tranny. couldnt see it due to my skid plate. there is a bad seal on the input of my t/case that allowed atf to flow into the t/case, thus overfilling it....
i had alrready dropped a friends 700r4 off to be rebuilt by this time..
so, $20 on new t/case seals, and $450 on a rebuild for the tranny, and all is (hopefully) well in the jeep world again...

i'll swap your running rich problem for my headaches?
keep at it, you'll get there...

martin

**ritjobbie** · 08-01-2007, 09:57 AM

Quote:

Originally Posted by Eclipse This

Oxygen sensor could cause it to run rich if i'm not mistaken. Just a thought.

I assume (yeah, I know) that the O2 sensor is working because it correctly recognizes the rich condition. I suppose it is easy enough to test some voltages to rule that out, huh? Sounds like my multimeter will get a workout tonight.

Beer, blues, and hot halogens in my garage tonight!

Thanks everyone for your help. Don't hesitate to give me any further suggestions, though. =)

learfxr · 08-01-2007, 10:13 AM

I vote for wires. My old Celica would hesitate when trying to accelerate, after many parts it was bad wires.

**ritjobbie** · 08-06-2007, 02:58 PM

Quote:

Originally Posted by learfxr

I vote for wires. My old Celica would hesitate when trying to accelerate, after many parts it was bad wires.

I just replaced wires, cap, rotor, and upstream O2 sensor. No dice--it still runs rich and seriously hesitates/loses power at 3k rpm.

Any other ideas before I bring it to a real mechanic?

EABiker · 08-06-2007, 03:16 PM

Strangely enough, a vacuum leak could be the culprit! If the O2 sensor reads a lean condition, caused by the vacuum leak, it will richen the mixture to overcompensate. Its worth a look!

bamato · 08-06-2007, 03:17 PM

When you say upstream O2 sensor... is there more than one?

Have you tried testing the vacuum system for leaks? What's the fuel pressure at on the fuel rail?

08-01-2007, 09:05 AM	#9
Eclipse This Registered User Join Date: Jan 2007 Location: Cincinnati Posts: 163 Profile Gallery Classifieds My Jeeps	Oxygen sensor could cause it to run rich if i'm not mistaken. Just a thought. __________________ '92 YJ 3.5" BlackDiamond / 1" Shackle / 285 Trxus '04 WJ Overland